Three Forming Processes of Elbow

Three major forming processes of elbow

a Hot push forming

Hot push elbow forming process is a process in which a one-to-one elbow pusher, a mandrel and a heating equipment are selected to make the blank sheathed on the die move forward under the push of the pusher, and in the process of movement, it is heated, expanded and zigzagged. The deformation feature of the hot push elbow is to determine the diameter of the tube blank according to the rule that the volume remains unchanged before and after plastic deformation of the metal data. The selected tube blank diameter is smaller than the elbow diameter. The deformation process of the blank is controlled by the core mold, so that the metal at the inner arc is compressed, compensated to other parts that are thinner due to the expanding, and then deep into the elbow with uniform wall thickness. The hot push elbow forming process has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, which is suitable for mass production. Therefore, it has become the first forming method for carbon steel and alloy steel elbows, and also used in the forming of some standard stainless steel elbows. The heating methods in the forming process include medium frequency or high frequency induction heating (the heating ring can be multi ring or single ring), flame heating and reverberatory furnace heating. The selection of heating method depends on the requirements of the forming products and the energy situation

b. Stamping forming

is the earliest forming process used to produce seamless elbows in batches. Now, the hot push method or other forming processes have replaced the production of commonly used standard elbows, but in some standard elbows, the production quantity is small, the wall thickness is too thick or too thin. It is still used when the product has special requirements. The pipe blank that is equal to the outer diameter of the elbow shall be selected for the stamping forming of the elbow, and the press shall be used to directly limit the forming in the die. Before stamping, the tube blank is placed on the lower die, and the inner core and end die are installed into the tube blank. The downward movement of the upper die is limited at the beginning, and the elbow is formed by the restraint of the outer die and the support effect of the inner die

Compared with the hot pushing process, the appearance quality of stamping forming is inferior to the former; The outer arc of the stamping elbow is in tension during forming, and there is no remaining metal in other parts to compensate, so the wall thickness at the outer arc is reduced by about 10%. However, because it is suitable for single piece production and has the characteristics of low cost, the stamping elbow process is mostly used for the production of small batches and thick wall elbows

Stamping elbow can be divided into cold stamping and hot stamping. Usually, cold stamping or hot stamping can be selected according to data properties and equipment. The forming process of cold kneading elbow is to use a one-to-one elbow forming machine to put the tube blank into the external mold. After the upper and lower molds are closed, the tube blank moves along the gap reserved by the internal mold and the external mold with the push rod to complete the forming process

The elbow made by cold kneading process of inner and outer molds has beautiful shape, uniform wall thickness and small scale error, so this process is often used for the forming of stainless steel elbow, especially thin-walled stainless steel elbow. The inner and outer molds used in this process require high precision; The requirements for wall thickness error of tube blank are also strict

c. Other forming methods. However, this process is relatively messy, time-consuming, and the forming quality is not as good as the aforementioned process, so it is less selected